(a) Field of the Invention
The present invention relates to a light guide plate having micro-reflectors applied on the backlight module of a liquid crystal display, and more particularly, to one that has an arc or sectorial recess at the bottom of the light guide plate to increase luminance of the light guide plate.
(b) Description of the Prior Art
Referring to FIG. 1 of the accompanying drawings for a schematic view of a micro-reflector 2 of a light guide plate 1 of the prior art, the micro-reflector 2 with rough surface is created by using the etching method on a bottom 12 of the smooth light guide plate 1. Rays of light 50 continuing to convey through the surface of the micro-reflector 2 create reflected rays 51 or refracted rays 52 of light in scattering fashion. The reflected rays 51 of light pass through an illuminating plane 11 of the light guide plate 1 when the angle of incidence of the reflected rays 51 is smaller than the critical angle; or are fully reflected back into the light guide plate 1 to continue passing on if the angle of incidence is greater than the critical angle.
FIG. 2 interprets coordinates illustrated in FIG. 3(a). FIG. 3(a) is a radar view of illuminating intensity of the rays of light leaving the illuminating plane 11 of the light guide plate 1 of the prior art. Wherein, the abscissa indicates a horizontal angle (HA) with the movement of angle turns from a normal direction 13 of the illuminating plane 11 into a direction 14 vertical to a light source 4; meanwhile, the ordinate indicates a vertical angle (VA). The movement of angle turns from the normal direction 13 of the illuminating plane 11 into a direction 15 in parallel with the light source 4. In FIG. 3(a), each closed curve represents a value of the illuminating intensity, which is defined as a luminous flux of each unit of a solid angle. There are ten closed curves as illustrated in FIG. 3(a), representing ten grades of illuminating intensity. As shown in FIG. 3(a), the distribution of the illuminating intensity from the light guide plate 1 of the prior art approximates the Lambertian distribution, i.e., the illuminating intensity indicates cosine distribution. When the illuminating intensity is converted into luminance value, the luminance value is equal in each direction.
Now referring to FIG. 3(b) for a perspective view of the illuminating intensity from the illuminating plane 11 of the light guide plate 1, the distribution of the illuminating intensity approximates spherical one, i.e., it resembles the Lambertian distribution to permit the observation changes of the illuminating intensity in angle or direction.
Furthermore, each of light guide plates as disclosed in Taiwan Patent Publication No. 575759, U.S. Pat. Nos. 6,629,764 and 6,755,545 is adapted with a linear light source. Each illuminating plane of the latter US patents makes in a wave form while each micro-reflector disclosed in all three citations is originated from a conic form of concave disposed on the bottom of the light guide plate. The micro-reflector of Taiwan Patent Publication No. 575759 is a semi-spherical or triangle cone, and a triangle when viewed sideways; the micro-reflector of U.S. Pat. No. 6,629,764, as indicated in its side view, is two consecutive triangles, similar to a capitalized letter M. The bottom of the light guide plate in the disclosed embodiment includes a slope. The micro-reflector in U.S. Pat. No. 6,755,545 is a single cone.
In general, rays of light reflected from the hollow inside of a conic form of the micro-reflector of a light guide plate are prone to scatter and prevent from easy concentration.